My 1998 wrangler has a top oil pressure of about 32,and at idle drops off to about 10 or 5. Some of the time it will stay at 30.Has anyone had
this problem in past? This jeep had 98,600 mile and it is a 4banger,2.5

Would it be a waste of time to replace oil pump.and if so where is best place to buy?

I have a 97 TJ 4 banger and my oil pressure gauge is useless. It's more than likely your oil pressure sending unit which is aroun $35 dollars at any auto parts store. Mine does the same thing, except I can drive for miles with it reading 0, but it's really working._________________My Morning Jacket

On the 2.5, your oil pressure should be:
idle (800 RPM) 25-35 psi
1,600+ RPM 37-75 psi
If it's not fluctuating, start by checking the sender, you could probably briefly short it (be careful - know how to do it on a CJ, just not sure if it'll work on a TJ or what effects it might have on the computer) to see if the sender or wiring is bad._________________Nothing to see here.